1. Field of the Invention
The present invention relates to an ink composition, and more particularly to an ink composition containing a micro-encapsulated UV absorber and a process for preparing the ink composition.
2. Background of the Invention
Generally, eight kinds of ink are required for full color inkjet ink printing and screen printing, that is, magenta ink, cyan ink, yellow ink, black ink, red ink, blue ink, green ink, and orange ink. Most inkjet ink printing uses water-based colorant, and most screen printing uses organic solvent-based colorant. For environmental concerns, water-based colorant has been a trend in recent years. In addition, new inks including light magenta ink, light cyan ink, light yellow ink, orange ink, and green ink have been developed for use in inkjet printing in recent years. A water-based ink composition includes at least one water-based colorant, water, an organic solvent, and other additives. A solvent-based ink composition includes at least one solvent-based colorant, an organic solvent, and other additives. An inkjet ink composition mainly uses a water-based colorant. Since a water-based colorant has better miscibility with water, water-fastness is inferior. Consequently, the printed image exhibits inferior water and light resistance. Generally, a colorant with good water resistance and light resistance is chosen to improve the overall water-fastness and light-fastness of an ink.
Presently, it is important to achieve superior water resistance and light resistance in color inkjet ink preparation. Colorant can be classified into dye and pigment. Water-based dye ink generally has inferior water resistance and light resistance for printed images. Therefore, a large amount of pigment-based ink, which has good water resistance and light resistance, has been developed. A pigment-based ink includes at least one pigment, water, an organic solvent, and other additives. Pigment-based inkjet ink has better water resistance and light resistance for printed images than water-based dye ink. However, pigment-based ink has inferior color brightness compared to dye-based ink. Therefore, a suitable dispersant and adhesive must be added to pigment-based ink. Moreover, pigment has a larger particle size, which easily generates precipitation and coagulation. This plugs the inkjet nozzle and lowers the printing quality.
Colorant fades gradually because a photochemical reaction occurs when the colorant is irradiated by light. This photochemical reaction is induced by absorbed light energy, and can be classified into photolysis, photo-synthesis, and photo-sensitization. Conventional methods to improve light resistance attempt to enhance the dye's resistance to light. For example, an indigo series dye grafted with halogen ions has a better resistance to light than a dye without halogen. In U.S. Pat. No. 6,176,909, a water-based UV absorber is added to an ink to enhance the light resistance. A colorant with better light resistance will exhibit limited ink color saturation. If a UV absorber is directly added to an ink, since the photochemical reaction is irreversible, the UV absorber will react with light continuously until it is completely consumed Thus, the ink cannot attain higher light resistance.